Ethan Couch, the teen in the "affluenza" drunk driving case in 2013, appears to have gone missing. A warrant has been issued for his arrest. Above, beer in a grocery store in New York City. Andrew Burton/Getty Images

Ethan Couch, a Texas teenager who gained infamy two years ago when he was sentenced to probation for killing four people in a drunk driving accident, went missing sometime this week, his probation officer said Tuesday. Couch's mother could also not be found, and an arrest warrant has been issued for Couch, now 18, CNN reported.

Couch's lawyers argued during his defense that he was a victim of "affluenza," a term that describes "the unhealthy and unwelcome psychological and social effects of affluence regarded especially as a widespread societal problem," according to Merriam-Webster. Such a defense, based on the idea that a young person's behavior can be blamed on the wealth of his or her parents, appeared legally unprecedented, but it nonetheless worked in Couch's favor. He was sentenced to 10 years' probation and was ordered to receive mental health treatment. Prosecutors had sought a maximum of 20 years in prison.

Under his probation terms, Couch was not to lose contact with his probation officer. It appears, however, that that is precisely what happened this week. One of his last suspected whereabouts was at a party where people were drinking alcohol, a video that surfaced on social media showed, CNN reported.

"We have recently learned that, for the last several days, the juvenile probation officer has been unable to make contact with Ethan or his mother, with whom he has been residing," attorneys for Couch said in a statement to KTVT in Forth Worth Tuesday. "It is our understanding that the court has issued a directive to apprehend to have Ethan detained [sic] because he is out of contact with his probation officer."

Couch could face up to 10 years in prison for violating the terms of his probation. The "affluenza" defense was widely derided and criticized, and after the trial, the psychologist who used the term while testifying on behalf of Couch, who was 16 at the time, said he regretted using it.

"Everyone seems to have hooked onto it," G. Dick Miller, the psychologist, told CNN in 2013. "We used to call these people spoiled brats."